A structure in which a circuit board to which electronic components such as a detection unit and a wireless device are attached is housed in a case (box member) made of a synthetic resin has been widely employed for conventional tire-state detection devices that detect the inner pressure of a tire.
For such a tire-state detection device, a method has been known in which a circuit board housed in a case having an open surface formed thereon is sealed with a sealant such as an epoxy-based resin (for example, Patent Literature 1). The sealing of a circuit board housed in a case with a sealant makes it possible to prevent or reduce failure of the tire-state detection device due to vibration or moisture.
The tire-state detection device having the enhanced water resistance as described above has been widely introduced for tires mounted on dump trucks used in mines. This is because a liquid (hereinafter, referred to as a coolant) dedicated to reduction of the increase in temperature during travel and to corrosion inhibition is injected into such a tire, and hence the tire-state detection device is required to have water resistance.